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Concerted regulation of nuclear and cytoplasmic activities of SR proteins by AKT

Abstract

Serine/arginine-rich (SR) proteins are important regulators of mRNA splicing. Several postsplicing activities have been described for a subset of shuttling SR proteins, including regulation of mRNA export and translation. Using the fibronectin gene to study the links between signal-transduction pathways and SR protein activity, we show that growth factors not only modify the alternative splicing pattern of the fibronectin gene but also alter translation of reporter messenger RNAs in an SR protein–dependent fashion, providing two coregulated levels of isoform-specific amplification. These effects are inhibited by specific small interfering RNAs against SR proteins and are mediated by the AKT kinase, which elicits opposite effects to those evoked by overexpressing SR protein kinases Clk and SRPK. These results show how SR protein activity is modified in response to extracellular stimulation, leading to a concerted regulation of splicing and translation.

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Figure 1: Activation of the PI 3-kinase pathway and its downstream target AKT is sufficient to alter fibronectin splice-site choice.
Figure 2: SF2/ASF and 9G8 are implicated in the growth factor– and AKT-mediated inclusion of fibronectin EDA.
Figure 3: SR protein kinase overexpression elicits opposite splicing effects to that of growth-factor (GF) treatment or AKT overexpression.
Figure 4: AKT can function as an SR protein kinase without changing SR protein localization.
Figure 5: Growth factors (GFs) and AKT alter translation of an ESE-containing mRNA.
Figure 6: Alteration of nuclear and cytoplasmic activities of SR proteins by growth factors (GFs) and the PI 3-kinase–AKT pathway.

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Acknowledgements

We thank M. de la Mata, J.P. Fededa, I. Schor, E. Petrillo and M. Alló for encouraging discussions as well as V. Buggiano and R. Fernandez for technical help. This work was supported by grants from Fundación Antorchas, Universidad de Buenos Aires, Agencia Nacional de Promoción Científica y Tecnológica and Consejo de Investigaciones Científicas y Técnicas (CONICET). M.B., F.P., T.T., M.J.M. and D.W. are recipients of doctoral fellowships from the CONICET. A.S., J.P.M, A.R.K. and O.A.C. are investigators of the CONICET. A.R.K. is an International Research Scholar of the Howard Hughes Medical Institute. We also acknowledge support from the Medical Research Council (J.F.C.) and the Caledonian Research Foundation (J.R.S.).

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Correspondence to Anabella Srebrow.

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Supplementary information

Supplementary Fig. 1

SiRNA against SF2/ASF and 9G8 completely blocks overexpression of T7-SF2/ASF and T7-9G8, respectively. (PDF 316 kb)

Supplementary Methods (PDF 109 kb)

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Blaustein, M., Pelisch, F., Tanos, T. et al. Concerted regulation of nuclear and cytoplasmic activities of SR proteins by AKT. Nat Struct Mol Biol 12, 1037–1044 (2005). https://doi.org/10.1038/nsmb1020

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